error Unexpected end of JSON input while parsing near '...
This is not a definitive answer but it looks like your global packages are corrupted in some way.
This bug may be caused by many different things. I suggest doing the following.
1 Install Node Version Manager (or NVM for Windows) and install Node version 10.16.1. This is enough for angular 9 and from my experience it is the most stable version for development. This should also change your NPM version so that may also help.
2 Uninstall global angular package npm uninstall -g @angular/cli
3 Force clear cache npm cache clean --force
4 Just to double check npm cache verify
5 You can also try clearing your %temp% and %roaming% AppData/npm-cache
6 install latest angular package npm install -g @angular/cli@<your-version>
7 if this error still occurs, consider using another shell
If this don't solve the problem try to manually locate the package.json file that is throwing an error and investigate.